Do I have to download a model to create a human being?
Makehuman is indeed an excellent tool.
To answer the second part of your question, and complete the precedent answer, concerning animation, you can import the model into blender by activating the mxh import plugin https://thomasmakehuman.wordpress.com/mhx2-documentation/import-into-blender/
Then, you can import .bhv mocap datas founded on the net (a lot of free ressources are availables) :


mocap.web.fh-koeln.de/webgl-search.php


(I can't put more than 2 links on this site because of my reputation wich is still too low, but a google search will do the job)

You then need to add the addon called MakeWalk, wich you can find on the makehuman site (same pb with the url, but you can find it on the thomasmakehuman site already listed). This will allow you to load and retarget your downloaded bhv files.